This story is the second of a series of 10 articles from Apolitical—an international platform for innovators in the public service and all those who care about effective government—about the best urban innovations around the world. The last one was about density. Stay tuned in two weeks for the next installment.

Cities are particularly blatant offenders because they depend on truck-, boat- and planeloads of food being transported in every morning to keep them alive. But their dense social mesh also makes them particularly able to fix the problem.

And giving food to hungry people—surprise surprise—makes society a lot better. One of the best examples is in the English former industrial town of Leeds, where food that would be thrown away from supermarkets goes to a big state school in a poor neighborhood. The school gets enough to feed all 600 pupils a nutritious breakfast and lunch for no extra cost to itself or to parents. Because the pupils aren't hungry or coming down off sugar rushes, there's less truancy, they behave better, and their exam scores have gone up.

But food banks and charities also end up with leftovers, so there's been an explosion in organizations, like Les Confitures de Dominique in Bordeaux, that turn unwanted fruit and veg into jams, smoothies, chutneys, and soups. In fact, there's a whole new industry of turning food waste into other food, like Toast Ale in London, which takes the unwanted bread ends that can't be used for prepackaged sandwiches and turns them into beer.

Aside from redirecting food to the needy, you can also use the Tinder principle—that you can solve a problem just by connecting the right dots—to bring unsold food together with people who'll buy it. There's a whole plethora of these apps, like FoodLoop, from Germany, which sends people push notifications when supermarkets reduce prices on food close to its sell-by date; or Too Good To Go, from Denmark, which connects diners to restaurants selling things like sushi and salad for rock-bottom prices at the end of the day.

The connection principle can also be used to break up food deserts—urban areas where you can buy processed, fried, dried, or canned food, but it's really hard to get cheap fresh fruit and vegetables. Naturally, these tend to be poor areas, and people's health suffers as a result. So in Chicago and Toronto, decommissioned buses have been turned into mobile markets, stopping outside clinics, schools, daycare centers, and housing complexes. Several U.S. states, like Colorado, are also sending out free lunch trucks during the school holidays, to make sure poor kids get nutritious meals. Join up those trucks with the food waste from supermarkets and you can use a social problem to power an improvement in deprived people's health.

A lot of food that gets wasted doesn't come from supermarkets or other big organizations though—it comes from households. So lots of cities are developing food-sharing networks, the most concrete version of which is a community fridge. In the Spanish city of Galdakao and across Germany and Austria, there are fridges where anyone can drop off food they're not going to use, and anyone can help themselves.

But there is a question about how many people will actually use these things and, even if they do, some things will still be thrown out: banana peel, chicken gristle, cheese rind. So how do you stop them going to landfill, where they rot and emit methane? In Philadelphia, the answer is to mandate that all new-build homes must have an in-sink shredder for food waste; the resulting slurry is turned into biogas, which is used to power the city's water treatment plant.

Ultimately, however, cities might be able to close the loop entirely. A new suburb of Amsterdam now being built plans to use that household waste to feed soldier flies. The flies feed fish, and the fish waste is used as the basis for aquaponic agriculture, growing fruit and vegetables. Since aquaponics can produce 10 times as much for the same amount of land, the suburb's developers expect to produce literally tons of organic food every year.

Taken together, these innovations—though not everyone wants to grow aquaponic tomatoes or use a community fridge—hold out the possibility that instead of going to all the effort of raising crops just to turn them into pollutants, we power our homes and fill our glasses with what we might once have thrown away.

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